1. Field of the Invention
This invention relates to an ignition enhancer coating composition for pyrotechnic propellants, especially those propellants suitable for use in inflating an inflatable device, such as a vehicle safety restraint.
2. Description of the Prior Art
Various pyrotechnic propellants have been prepared for generating a gas upon combustion in order to inflate an air bag or similar safety restraint in a vehicle so as to restrain movement of an occupant in the event of a sudden deceleration of the vehicle, such as caused by a collision. In order to be employed as a pyrotechnic gas generating composition for inflatable occupant restraints, several criteria must be met. The pyrotechnic must be capable of producing non-toxic, non-flammable and essentially smokeless gases over a wide variety of temperatures and other environmental conditions. The gases that are generated must be totally ignited at a sufficiently low temperature so as not to destroy the restraint or injure the occupant. The pyrotechnic must also be safe to handle and must be capable of generating a substantial amount of gas within a very short period of time, e.g., less than about 100 milliseconds.
In order to achieve total ignition and combustion of the pyrotechnic formulation various additional ingredients have been employed. Such ingredients include copper chromite and iron oxide as taught in U.S. Pat. No. 3,933,543, or a mixture of inorganic oxidizer compounds and an oxygen bearing organic fuel as taught in U.S. Pat. No. 3,964,255. These ingredients are conventionally taught as being admixed with the pyrotechnic propellant before the propellant is pressed into pellets. Although such admixtures are effective to a degree, there is still a need for a more effective ignition enhancer as well as a need for a more effective combination of propellant and ignition enhancer.